How can I build a bike very cheaply from parts? (including how-to sources and important details)

I want to build a bike, probably a fixie since I never used the gears on my bike before and I imagine it would be a simpler mechanism, but I want it to be very cheap.

I am willing to do work and buy parts but past experiences have taught me that trying to fix something with parts can sometimes cost as much as a new, finished product. My goal is $50, $75 max, so a solid, simple bike.

What resources, like sites or books, will help? Also, whats a good place to find bike scrap?